1. The Softening Process: As hard water passes through the permutit bed, the following exchange occurs:
$$Na_2Z + Ca^{2+} \to CaZ + 2Na^+$$
Over time, the sodium ions in the permutit are replaced by calcium and magnesium ions, and the permutit becomes "exhausted" as it loses its ability to soften water.
2. The Regeneration Process: To reuse the exhausted permutit ($CaZ$ or $MgZ$), it must be converted back to its sodium form. This is achieved by treating it with a concentrated (brine) solution of
sodium chloride ($NaCl$)[cite: 74].
3. Chemical Reaction for Regeneration: $$CaZ + 2NaCl \to Na_2Z + CaCl_2$$
The calcium chloride formed is washed away, leaving the bed of regenerated sodium permutit ($Na_2Z$) ready for the next cycle of water softening[cite: 74].